1. Field of the Invention
The present invention relates to a printed circuit board that is preferably used for electronic devices such as video cameras.
2. Description of the Related Art
The structure of a prior-art printed circuit board is described below with reference to FIGS. 4 and 5. In the figures, an insulating board 21 formed of a flexible material has a rectangular base portion 22 comprising stationary contacts (not shown in any figures) and a leading portion 23 formed generally in the shape of a letter xe2x80x9cLxe2x80x9d in its entirety.
The leading portion 23 may be formed generally in the shape of a letter xe2x80x9cLxe2x80x9d in order to avoid contacting with electric parts (not shown in any figures) provided in the electric device, mounting members (not shown in any figures) or the like. The leading portion 23 is provided with a curved portion 23a bent in the shape of a letter xe2x80x9cLxe2x80x9d, cable portions 23b connected to both sides of the curved portion 23a and formed to be the same as the curved portion 23a in width, and a delivery portion 23c provided at an end of the cable portion 23b. 
A plurality of trace patterns 24 formed of silver each have a bent portion 24a bent in the shape of a letter xe2x80x9cLxe2x80x9d, straight trace portions 24b connected to both ends of the bent portion 24a and having the same pattern width as that of the bent portion 24a, and a straight connecting portion 24c provided at an end of the trace portion 24b. 
The trace patterns 24 are formed on the leading portion 23 by screen-printing in parallel to each other, with the bent portion 24a disposed at the curved portion 23a of the leading portion 23 of the insulating board 21, the trace portion 24b disposed at the cable portion 23b and the base portion 22, and the connecting portion 24c disposed at the delivery portion 23c, respectively.
The trace portion 24b formed on the base portion 22 is connected to the stationary contacts (not shown in any figures) formed on the base portion 22 as an electrically conductive pattern.
The printed circuit board fabricated as such allows the connecting portion 24c provided at the delivery portion 23c to be connected with a connector (not shown in any figures), being adapted that an external current flows into the printed circuit board through the connecting portion 24c or a current from the printed circuit board is delivered outwardly through the connecting portion 24c. 
To this end, the connecting portion 24c is a critical one and therefore a high accuracy is required of the screen-printing at the connecting portion 24c. 
A prior-art method for fabricating a printed circuit board by means of screen-printing is implemented as shown in FIG. 6. That is, the insulating board 21 is placed and held on a mounting stage 25, and thereafter a meshed print mask 26 is placed on the insulating board 21.
Then, silver paste 27 is applied to the print mask 26, and thereafter a squeezer 28 is moved in the direction indicated by arrow A to form a plurality of trace patterns 24 by printing on the insulating board 21.
That is, in FIGS. 4 and 5, the squeezer 28 is to move along the arrow A.
At this time, the connecting portion 24c is first formed by means of printing, then the trace portion 24b is printed, and thereafter the bent portion 24a is formed by means of printing.
On the other hand, at the time of this printing, the delivery portion 23c of the leading portion 23 is located closer to the initial position of the squeezer 28. In addition to this, the connecting portion 24c or part of the trace pattern 24, formed in the shape of a straight pattern, is printed in a manner such that the squeezer 28 is to move in the direction of this straight pattern.
In other words, the squeezer 28 is moved in the direction of the straight pattern. This makes it possible to considerably reduce patchy portions of the silver paste 27 and thereby provide highly accurate printing at the connecting portion 24c. 
In addition, the bent portion 24a or part of the trace pattern 24 is printed in a manner such that the squeezer 28 is moved in a direction generally perpendicular to the direction of the pattern.
At this time, patchy portions 29 (refer to FIG. 5) of the silver paste 27 are likely to occur at the bent portion 24a due to air bubbles or the like that are produced at the corners of ink-penetrating portions of the print mask 26 for forming the bent portion 24a. 
As the electronic devices are reduced in size, it is required to reduce the size of the printed circuit board. This has lead to a narrower spacing between the trace patterns 24 and a smaller pattern width thereof, which has in turn presented the possibility of causing a break in a narrowed bent portion 24a due to the presence of a patchy portion 29 or the like.
The prior-art printed circuit board is provided with the trace pattern 24 having the same pattern reduced in width at both the bent portion 24a and the trace portion 24b. This presents a problem of causing a break at the bent portion 24a due to the presence of a patchy portion 29 or the like upon forming the trace pattern 24 by printing.
It is therefore an object of the present invention to provide a highly reliable printed circuit board that provides reduced breaks at the bent portion of the trace pattern.
As first means for solving the aforementioned problems, the present invention provides a printed circuit board which comprises an insulating substrate and a trace pattern formed by means of screen-printing on the insulating substrate and provided with a bent portion and trace portions connected thereto. The printed circuit board is adapted that the pattern width of the bent portion is wider than that of the trace portions located near both sides of the bent portion.
As second means, the present invention provides the printed circuit board adapted that the trace pattern is formed by means of screen-printing in such a direction as to firstly form the trace portions connected to the bent portion and thereafter to form the bent portion by printing.
Furthermore, as third means, the present invention provides the printed circuit board with the insulating substrate comprising a curved portion and cable portions connected to both ends of the curved portion. The insulating substrate is provided with a plurality of the trace patterns, with the width of the curved portion made wider than that of the cable portion and the bent portion located at the curved portion as well as the trace portion located at the cable portion.
Furthermore, as fourth means, the present invention provides the printed circuit board adapted that a connecting portion having the shape of a straight pattern is provided at one end of the trace portion connected to the bent portion, and the trace pattern is formed by means of screen-printing along the longitudinal direction of the straight pattern.